1. Field of the Invention
The present invention relates to an electric pressurizing rice cooker, and more particularly to a steam exhaust system of an electric pressurizing rice cooker, which can control the pressure in a cooking vessel and simultaneously can prevent the pressure in the cooking vessel from excessively elevating during the cooking process.
2. Description of the Related Art
An electric rice cooker is an appliance for cooking rice which utilizes electricity as a heating source. Especially in an electric pressurizing rice cooker, the interior of a cooking vessel is maintained at a relatively high pressure, higher than that of the atmosphere, so that the cooking in the cooking vessel can be rapidly performed.
As shown in FIG. 1, a conventional electric pressurizing rice cooker includes a cooking vessel 10, a cooker housing 12 in which the cooking vessel 10 is accommodated, a lid 14 for opening and closing the cooker housing 12, an electric system for heating/warming the cooking vessel 10, and a steam exhaust system for controlling the pressure in the cooking vessel 10 during the course of cooking.
Referring to FIG. 2, the electric system includes a working coil 16 and a heater 18 disposed in the cooker housing 12. The working coil 16 generates induced currents for cooking, and the heater 18 functions to generate relatively less heat for warming rice in a so-called warming mode.
Meanwhile, the steam exhaust system includes a solenoid valve 20 and a poise valve 30. The solenoid valve 20 is automatically opened to lower the pressure in the cooking vessel 10 when a predetermined amount of time has passed after the cooking is initiated. The poise valve 30 is opened when the pressure in the cooking vessel 10 exceeds a predetermined value during the course of cooking to prevent the pressure in the cooking vessel from excessively elevating, and simultaneously to maintain the pressure constant.
As shown in FIG. 3, the solenoid valve 20 is disposed at a top plate 141 of the lid 14, and includes a first steam exhaust pipe 22 interconnected to the exterior of a top cover 142, a diaphragm 24 for opening and closing a steam hole 22a in the first steam exhaust pipe 22, a plunger 26 assembled with the diaphragm 24, and a solenoid coil 28 for actuating the plunger 26.
The poise valve 30 as described above includes a second steam exhaust pipe 32 penetrating through the lid 14, and a pressurizing weight 34 disposed at the upper end of the second steam exhaust pipe 32 outside of the lid 14.
The pressurizing weight 34 supports a valve pin 35 received through the top of the pressurizing weight 34, in such a manner that the valve pin 35 can open and close the upper end of a steam exhaust channel 32a of the second steam exhaust pipe 32. The pressurizing weight 34 has an exhaust port 34a formed through the bottom of the pressurizing weight 34, through which steam can be exhausted.
Hereinafter, will be described the cooking operation by the electric pressurizing rice cooker having the construction as described above.
At first, the working coil 16 induces eddy current at the cooking vessel 10, which slowly heats the cooking vessel 10, so as to promote a so-called soaking process during which water is absorbed in each grain of rice. After the soaking process is performed for a predetermined period, the cooking vessel is heated at a high temperature, so that the temperature of the water in which the rice is immersed is rapidly elevated to the boiling point.
In this case, the upper end of the cooking vessel 10 is firmly coupled to the lower surface of the top plate 141 by an assembling device (not shown), and the solenoid valve 20 and the poise valve 30, which are parts of the steam exhaust device, are maintained in a closed position. Accordingly, when the boiling process is initiated and the water begins to boil, steam is generated to make the pressure in the cooking vessel 10 higher than that in the atmosphere.
Due to the increase of the pressure in the cooking vessel 10, the temperature in the cooking vessel 10 elevates beyond the boiling point of 100.degree. C. at the normal atmospheric pressure, so that the rice is cooked faster than at normal atmospheric pressure.
When the boiling process during a predetermined period is completed, a steaming process is initiated in the state where the heating is stopped. In the steaming process, the rice is steamed, without being separately heated, by the steam remaining in the cooking vessel after the boiling process, usually after the water is completely boiled away.
After the steaming process is completed for a predetermined amount of time, the steam in the cooking vessel 10 is exhausted by the operation of the solenoid valve 20, so that the pressure in the cooking vessel 10 is lowered. In this state, a warming process is initiated in which the cooking vessel 10 is heated by a relatively low degree of heat, at a relatively low, constant temperature by means by the heater 18.
In this case, when the solenoid valve 20 is operated, electric power is first applied to the solenoid coil 28 by a control section (not shown). Then, magnetic force generated by the solenoid coil 28 actuates the plunger 26, which elastically deforms the diaphragm 24 to open the steam hole 22a. Then, the steam in the cooking vessel 10 is exhausted through the opened steam hole 22a and steam channel of the first steam exhaust pipe 22 interconnected to the steam hole 22a.
Further, when the pressure in the cooking vessel 10 becomes higher than a predetermined reference value during the course of the cooking operation, the poise valve 30 is operated to exhaust a desired amount of steam in the cooking vessel 10, thereby preventing an excessive elevation of pressure.
Hereinafter will be described, in detail, the operation of the poise valve 30 as described above.
First, before the pressure in the cooking vessel 10 reaches a predetermined reference value, the steam exhaust channel 32a of the second steam exhaust pipe 32 is maintained closed by the valve pin 35. This is because the valve pin 35 is forced downward due to the weight of the pressurizing weight 34 so as to block off the steam exhaust channel 32a. When the pressure in the cooking vessel 10 exceeds the reference value, that is, the weight of the pressurizing weight 34, the valve pin 35 is pushed upward causing the pressurizing weight 34 to vibrate and become cooked. The steam exhaust channel 32a is then opened, whereby the steam in the cooking vessel 10 is exhausted through the exhaust port 34a of the pressurizing weight 34. The pressure in the cooking vessel 10 is then lowered below the reference value.
When the pressure in the cooking vessel 10 is lowered below the reference value, the pressurizing weight 34 recovers its balance due to its construction, so that the valve pin 35 again blocks off the steam exhaust channel 32a, thereby preventing an excessive pressure reduction. The repetition of the above process maintains the pressure in the cooking vessel 10 in a predetermined range during the cooking process.
In the conventional electric pressurizing rice cooker as described above, effective cooking is achieved through the safe operation of and the pressure control of the steam exhaust system.
However, according to the conventional technique as described above, since the poise valve 30 maintains the pressure in the cooking vessel 10 at a predetermined level by means of the operation of the pressurizing weight 34 during the cooking operation, only pressurized cooking at a single predetermined pressure can be performed. Accordingly, there is a restriction in the conventional electric pressurizing rice cooker, in that it is impossible to cook food into various states according to the user's tastes by controlling the pressure in the cooking vessel 10.
Further, the conventional electric pressurizing rice cooker is also problematic, in that its manufacturing cost is relatively high, since the solenoid valve 20 having a complicated construction and requiring a relatively large number of parts is necessary in addition to the poise valve 30 in the conventional cooker.